Pen type drug delivery devices have application where regular injection by persons without formal medical training occurs. This is increasingly common among patients having diabetes where self-treatment enables such patients to conduct effective management of their disease.
In certain types of medication delivery devices, such as pen type devices, cartridges of medication are used. These cartridges are housed in a cartridge holder or cartridge housing. Such cartridges include a bung or stopper at one end. At the other end of the cartridge, the cartridge comprises a pierceable seal. To dispense a dose of medication from such a cartridge, the medication delivery device has a dose setting mechanism that uses a spindle to move in a distal direction towards the cartridge and to press a distal end of the spindle against the bung. This expels a certain set dose of medication from the cartridge. As medication runs low, a user may attempt to set a dose that exceeds the amount of medication left in the cartridge. In order to insure dose accuracy, it is important that a drug delivery device is designed to not allow a user to dial a dose that is greater than the amount of medication remaining in the cartridge. As some users may apply a large turning force (i.e., a large torque load) when attempting to dial a dose that exceeds the amount of medication left in the cartridge, it is important that the drug delivery device be able to withstand a large force.
There is, therefore, a general need to take these perceived dose accuracy issues into consideration when designing either resettable or non-resettable drug delivery devices, such as pen type drug delivery devices.